3.14.4 Accumulation Charge

Note: This section is still subject to verification and may be changed or removed in future versions.

The calculation for accumulation region charge are performed only if both the switches $CAPMOD$ and $BULKMOD$ are set to 1, i.e. for a bulk-substrate device only. This introduces a computational effort equal to the calculation of surface potential on the source side. For calculation of accumulation region charge, the device is treated as intrinsically doped i.e. $NBODY_i = n_i$. However additional flexibility is introduced through a separate effective oxide thickness ($EOTACC$) and a separate flatband voltage value (through $DELVFBACC$) for the accumulation side calculations.

Voltage limiting for $V_{ge} > V_{fb}$ region:

$T_1 = -V_{ge} + \Delta \phi - \dfrac{E_g}{2} + DELVFBACC \qquad (3.407)$

where $\Delta \phi$ is the work function difference between the gate and semiconductor materials.

$V_{gsfbeff,acc} = \begin{cases} \dfrac{1}{2} \Big[ T_1 + \sqrt{T_1^2 + 4 \times 10^{-8}} \Big] - \dfrac{E_g}{2} &\text{for } GEOMOD \ne 3 \\ \\ \dfrac{1}{2} \Big[ T_1 + \sqrt{T_1^2 + 4 \times 10^{-8}} \Big] - V_{t0,acc} &\text{for } GEOMOD = 3 \end{cases} \qquad (3.408)$